Controlling premature curing of vulcanizable halogen-containing polymers

Abstract: A process of reducing the effects of moisture during storage prior to vulcanization of a vulcanizable halogen-containing polymer composition containing water, comprising blending before storage, into said vulcanizable composition, a thioester derivative of 2,5-dimercapto-1,3,4-thiadiazole crosslinking agent and glycerin, whereby the scorch time of the vulcanizable compound is not significantly affected by the water content of said composition. In addition, a vulcanizable halogen-containing polymer composition comprising a thioester derivative of the crosslinking agent and glycerin, and a dry pourable powder cure premix composition comprising the crosslinking agent, glycerin and a pourable siliceous finely divided filler.

Description: This invention relates to vulcanizable halogen-containing polymer compositions and their preparation. In the production of vulcanized halogen-containing polymer, the use of mercapto compounds as crosslinking agents, and the use of various other additives to improve curing speed, strength and stability of the vulcanizates are known. See the hereinafter referred to patents, all of which are incorporated herein by reference. Vulcanization by these conventional techniques tends to be erratic and not reproducible if a mixed uncured composition has been stored. Scorching of the fresh unvulcanized (green) material takes place during storage, even at room temperature, which affects the cure conditions required to manufacture useful parts. Scorching is thought to be the premature start of the curing reaction, including some crosslinking, which affects subsequent curing of the material. This may reduce the cure time to the point where the compound cures before the part is properly molded. Scorched compound may be partially gelled and have a higher viscosity than unscorched compound. This may reduce flow so that molds cannot be filled completely. Often improperly cured products must be discarded. It has been observed that differences in water content of the compositions appear to be largely responsible for the scorching. Water may be absorbed by the green compositions from humidity in the air, or by inclusion in the individual ingredients, notably carbon black. Such vulcanizable compositions absorb water in normal storage, usually in an amount ranging from about 0.05% to about 2% by weight depending on the relative humidity and the length of storage. U. S. Patent No. 4,128,510 describes the use of broad classes of derivatives of 2,5-dimercapto-1,3,4-thiadiazole as crosslinking agents for halogen-containing polymers to produce vulcanizates of increased strength and stability. U. S. Patent No. 4,288,576 discloses the use as the crosslinking agent of 2,5-dimercapto-1,3,4-thiadiazole in the presence of certain basic materials to produce vulcanizates of good stability. U. S. Patent No. 4,482,681 shows the use of a crosslinking system for halogen-containing polymers made up of a polymercapto compound or an ester derivative thereof as the crosslinking agent, a basic material and a hydrated salt to increase the rate of crosslinking. U. S. Patent No. 4,745,147 discloses curable compositions comprising chlorinated polyethylene, a polymercapto compound, an aliphatic polyhydroxy compound, an inorganic acid acceptor and an initiator which is an amine, or a quaternary ammonium salt or a quaternary phosphonium salt. Aliphatic polyhydroxy alcohols mentioned include 2,2-dimethyl-1,3-propanediol, ethylene glycol, glycerol, 1,2-propanediol, dipentaerythritol and pentaerythritol. It has been found that water-induced scorching of halogen-containing polymer vulcanizable compositions can be masked, greatly decreasing the effect of water-induced scorching by (1) selecting a thioester derivative of 2,5-dimercapto-1,3,4-thiadiazole as the crosslinking agent and (2) including in the compositions glycerin (GLY). According to a first aspect, there is provided a process for reducing the effects of moisture during storage prior to vulcanization of a vulcanizable halogen-containing polymer composition containing water, comprising blending into said vulcanizable composition prior to storage, 0.1-20 parts by weight of a thioester derivative of 2,5-dimercapto-1,3,4-thiadiazole crosslinking agent and 0.1-20 parts by weight of glycerin, the amounts of the thioester derivative and glycerin being based upon 100 parts by weight of the halogen-containing polymer, the composition containing at least 0.05% by weight of water after storage at the start of vulcanization; whereby the scorch time t s 2 of the vulcanizable composition does not decrease by more than 30% after storage at ambient conditions of about 23 °C and 50% relative humidity for 1 day as compared to the t s 2 of the unstored composition. Preferably, according to this process, the cure time of the vulcanizable compound is not significantly affected by the water content of said composition. The invention is also directed to a vulcanizable halogen-containing polymer composition comprising 0.1-20 parts by weight of a thioester derivative of 2,5-dimercapto-1,3,4-thiadiazole crosslinking agent, 0.1-20 parts by weight of glycerin, the amounts of the thioester derivative and glycerin being based upon 100 parts by weight of the halogen-containing polymer, and at least 0.05% by weight of water; whereby the scorch time t s 2 of the vulcanizable composition does not decrease by more than 30% after storage at ambient conditions of about 23°C and 50% relative humidity for 1 day as compared to the t s 2 of the unstored composition. Preferably, said composition has a cure time that is not significantly affected by the presence of water in the composition. Preferably, the crosslinking agent is 2-mercapto-1,3,4-thiadiazole-5-thiobenzoate. Any saturated or unsaturated vulcanizable halogen-containing polymer, i.e. containing at least about 1 % to 60 % or more by weight of halogen, may be employed in the crosslinkable compositions of this invention. Preferred halogen-containing polymers are homopolymers of epichlorohydrin; copolymers of epichlorohydrin and ethylene oxide or propylene oxide; terpolymers of epichlorohydrin, ethylene oxide or propylene oxide, and an unsaturated alkylene oxide; polychloroprene; chlorosulfonated polyethylene; chlorinated high density polyethylene; copolymers of alkyl acrylate and chloroalkyl acrylate; poly(vinyl fluoride); poly(vinyl chloride); poly(vinylidene chloride); and chlorobutyl rubber and bromobutyl rubber. A preferred vulcanizable halogen-containing polymer is chlorinated polyethylene polymer. Other preferred polymers are epichlorohydrin polymers, copolymers and terpolymers, polyacrylate rubber (polyalkyl acrylates containing a low concentration of chlorine as a crosslinking site), polychloroprene rubber, chlorobutyl rubber and bromobutyl rubber. In addition, crosslinkable blends of halogen-containing polymers or halogen-containing polymers blended with nonhalogen-containing polymers may be used in the compositions and process of this invention. Examples of such non-halogen polymers are ethylene-propylene elastomers, nitrile elastomers, polyacrylate rubbers (non-halogen containing), and styrene-butadiene rubbers. The only requirement is that there be sufficient halogen-containing polymer present in the blend to effect crosslinking. Herein, all parts are per hundred parts by weight of the halogen-containing polymer (phr) and percentages are by weight of the total composition except as otherwise noted. 0.1 parts per hundred parts of halogen-containing polymer (phr) to 20 phr of glycerin is added to the unvulcanized compositions of the present invention, preferably from about 0.5 phr to 10 phr, and more preferably from about 1 phr to about 5 phr. The amount of thioester derivative of 2,5-dimercapto-1,3,4-thiadiazole crosslinking agent added is 0.1 phr to about 20 phr, preferably from about 0.5 phr to about 5 phr. In practicing the present invention it may, in some cases, be preferable to add a small amount of conventional stabilizer. Total stabilizer in the present invention composition preferably is in the range of about 0.1 phr to 5 phr or more. Exemplary of the most preferable stabilizers are phenyl-β-naphthylamine, di-β-naphthyl-p-phenylenediamine, sym-di-β-naphthyl-p-phenylenediamine, styrenated diphenylamines, N-isooctyl-p-amino-phenol, the reaction product of diphenylamine and acetone, polymerized trimethyldihydroquinoline, 4,4'-thio-bis(6-tert-butyl-m-cresol), the reaction product of crotonaldehyde and 3-methyl-6-tert-butyl-phenol, nickel dibutyldithiocarbamate, the zinc salt of 2-mercapto-benzimidazole, and nickel dimethyldithiocarbamate. An acid acceptor is preferably used in conjunction with the thioester derivative of 2,5-dimercapto-1,3,4-thiadiazole in the crosslinking process of this invention. An acid acceptor is a basic material or a material which will become basic on heating to the crosslinking temperature. Typical useful inorganic materials are basic metal oxides and hydroxides and their salts with weak acids, such as, for example, magnesium oxide, magnesium hydroxide, calcium oxide, calcium hydroxide, barium oxide, barium carbonate, lead oxides, lead acetate, sodium phenoxide and sodium acetate. The acid acceptor is added broadly, preferably from about 0.25 phr to about 50 phr, more preferably from about 0.5 phr to about 50 phr, and most preferably from about 1.0 phr to about 20 phr of the vulcanizable composition. In the compositions of the present invention, an accelerator of the well-known types containing aliphatic or aromatic amine or quaternary nitrogen groups may be used. Preferably about 0.5 to 3 phr of accelerator is used. Particularly useful accelerators are the reaction products of butyaldehyde and aniline, and tetrabutylammonium bromide. Other ingredients commonly used in rubber vulcanization can be included, for example, fillers, extenders, pigments, plasticizers, softeners, etc. The presence of a filler and, in particular, carbon black gives very advantageous results. The crosslinking agent and other ingredients can be incorporated or admixed with the polymer in any desired fashion. For example, they can be uniformly blended with a polymer by mixing in a high intensity internal mixer, such as a "Banbury" mixer; or by simply milling on a conventional rubber mill to prepare the green compositions of the present invention. By this means, the agents are uniformly distributed throughout the polymer and uniform crosslinking is effected when the composition is thereafter subjected to curing heat. It is generally preferable to mix at temperatures of 76-121°C (from about 170°F to about 250°F) because the compositions are usually relatively scorch-resistant below 121°C (about 250°F) in the short mixing time. Other known methods of admixing the composition are also useful. While all of the ingredients are normally blended in a single operation, often it is possible to rework the initially blended compositions of the present invention to change the relative amounts of the ingredients or even to add an ingredient. For instance, if a sample of a composition of the instant invention made using GLY is tested prior to use in production and the scorch is too short for processing in a specific production operation, then adjustments can be made in the concentration of crosslinker and/or accelerator (e.g., amine accelerator) to increase the scorch time. Compositions prepared following prior techniques generally can not be reworked because they are likely to scorch. Consequently, this invention is also directed to a process of reworking a vulcanizable halogen-containing polymer composition comprising sequentially blending before storage, into said vulcanizable composition, a thioester derivative of 2,5-dimercapto-1,3,4-thiadiazole crosslinking agent and glycerin, storing the vulcanizable halogen-containing polymer composition for one or more days, testing a sample of the vulcanizable halogen-containing polymer composition for at least one property selected from the group consisting of the cure rate or the scorch rate of the vulcanizable halogen-containing polymer composition and the physical properties of the vulcanized halogen-containing composition, and reformulating the vulcanizable halogen-containing polymer composition. According to a preferred embodiment, reformulating comprises adjusting the concentration in the vulcanizable halogen-containing polymer composition of at least one member selected from the group consisting the thioester derivative of 2,5-dimercapto-1,3,4-thiadiazole crosslinking agent and glycerin. According to another preferred embodiment, when the composition comprises one or more additives selected from the group consisting of accelerators, acid acceptors, binders, stabilizers, fillers, extenders, pigments, plasticizers, and softeners, and the reformulating comprises adjusting the concentration of the one or more additive in the vulcanizable halogen-containing polymer composition. The conditions under which the crosslinking is effected can be varied over a wide range. Preferably the crosslinking temperature will be within the range of broadly from 121°C (about 250°F) to over 218°C (425°F) and more preferably from about 171°C (340°F) to about 204°C (400°F). The time will vary inversely with the temperature and will preferably range from about 10 seconds to 24 hours, more preferably from about 2 to about 10 minutes. While the crosslinking process can be conducted in air at atmospheric pressure, it will generally be conducted in a metal mold or in a steam autoclave at the required temperature. For ease of incorporating the crosslinking agent into the crosslinkable polymer mixture, it may be desirable to formulate the thiadiazole derivative as a concentrate in a binder or carrier which can be added, along with the other ingredients, in small amounts to the polymer composition without adverse effect on the properties of the crosslinked composition. Particularly advantageous binders or carriers are polymers which may or may not be crosslinkable by the crosslinking agent. Suitable binders for the concentrate are, for example, ethylene-propylene rubber, ethylene-propylene terpolymers, styrene-butadiene rubber, natural rubber, low density polyethylene, amorphous polypropylene and polyisobutylene. Other suitable binders or carriers for use in the preparation of such easily handled concentrates are waxes, resins, or other low-melting solids. Typical useful materials are paraffin wax, stearic acid, microcrystalline wax, rosin, rosin esters and hydrocarbon resins. Concentrations of the thiadiazole derivative can vary from less than 30% to more than 90%, preferably from about 50% to 80%. In the final prevulcanization green mix additional amounts of one or more of the active curing compounds may be added to give the desired vulcanization and vulcanizate properties. The acid acceptor should not be incorporated in the concentrate lest it decompose the thiadiazole derivative. Another highly effective technique for simplifying final formulation is to prepare a dry pourable powder cure premix composition comprising the 2-mercapto-1,3,4-thiadiazole-5-thiobenzoate crosslinker, the GLY and a pourable siliceous finely divided material, such as silica, talc and clay. Thus, this invention is also directed to a composition in the form of a dry pourable powder cure premix composition for inclusion in a halogen-containing vulcanizable polymer composition, comprising a thioester derivative of 2,5-dimercapto-1,3,4-thiadiazole crosslinking agent, glycerin and a pourable siliceous finely divided filler. Preferably, the finely divided filler is selected from the group consisting of silica, talc and clay. This premix will contain enough of the filler to give a pourable powder formulation. Amounts of filler preferably are about 10-50% by weight of the formulation. The remainder of the formulation usually is crosslinker and GLY in the desired proportions for the particular usage. Other inert additives may also be included. This pourable premix avoids the handling of liquids when mixing these ingredients into the green prevulcanization products. The vulcanizable compositions of this invention exhibit more uniform scorching over a prolonged period of storage, little affected by the moisture content of the mixture after storage. Also, scorching during storage is decreased. The present invention compositions, with changes in ingredients and their amounts, may give mixtures of different scorch characteristics. However, batches of the same ingredients in the same amounts will exhibit substantially the same scorch characteristics irrespective of the moisture content of the initial ingredients, the storage relative humidity, and length of storage. Consequently, these compositions give vulcanizates of highly uniform curing characteristics and cured physical properties when vulcanized under the same conditions. For instance, the fabricator can store a batch of green composition for a number of days, such as 1, 4, 7, 14 or more, and regardless of moisture absorption by the composition, will be able to process the unvulcanized composition to meet product requirements. In the drawings, Figure 1 is two graphs of a conventional control composition containing no GLY, showing the effect of aging in a dry or humid atmosphere on cure time and scorch time. Figure 2 is two graphs of a composition of the present invention containing GLY, showing the effect of aging in a dry or humid atmosphere on cure time and scorch time. Figures 3-6 are ODR cure and cure rate plots for Example 10 and are explained below. The following examples illustrate the preparation of the vulcanizable compositions and vulcanizates thereof, properties of the vulcanizates, and the effect of water on scorching and the masking of the scorching in vulcanizates made from the present compositions. All compositions of the examples are given in parts by weight per hundred parts of the halogen-containing polymer content (phr) except where indicated otherwise. In the following examples the ingredients were mixed using standard procedure on laboratory mixers. Rubber physical properties were determined following ASTM D412-92. The extent of cure was measured from data obtained using a Monsanto oscillating disk rheometer (ODR) following the procedure of ASTM D2084-92. Scorch time was reported as t s 2, the time in minutes from closure of the ODR cavity until the torque increased 0.23 Nm (2 lbf.in) above the minimum torque, which occurs a short time after cavity closure when the applied heat decreases the viscosity and lowers the torque before significant crosslinking occurs. Shorter scorch times during curing indicate that more scorch has taken place before curing, as compared to unaged composition. Thus, a reduction in the rate of scorching increase during storage is shown by a longer scorch time (t s 2). Cure time was reported as t 90 , the time in minutes from closure of the ODR to reach 90% of increase from minimum to maximum vulcanization (cure) torque. Another advantage of this invention is the reduced time to cure show by the t 90 data. Curing of the present invention compositions is not significantly affected by the presence of normal amounts of water absorbed during storage, typically at least about 0.05% by weight, more typically from about 0.05 to about 2% by weight, and often about 0.2% to 2% by weight of the composition. This is indicated by the scorch times and cure times of the compositions which are not significantly affected by the water content of the compositions. Scorch time and cure time are quantified in terms of the performance of the composition under curing conditions. Thus, as the terminology is used herein, scorch time and cure time of a composition are not significantly affected by the presence of water when in curing using the conditions of Example 1 (ODR at 177°C (about 350°F), 3° arc and 100 cpm), the scorch time and cure time (t s 2 and t 90 as herein defined) are not significantly changed by water absorption during storage. "Not significantly changed", as used herein, means that neither t s 2 nor t 90 of the composition during such curing decrease (as compared to the t s 2 and t 90 of the green, substantially moisture-free, unstored composition) after storage at ambient conditions of about 23°C and 50% relative humidity of the composition for 1, 4 and 7 days by more than 30%, 50% and 75%, respectively; preferably, not more than 20%, 30% and 40%, respectively; and, most preferably, not more than 5%, 10% and 15%, respectively. (In other words, the compositions of this invention are capable of being stored for these periods of time with no more than the percentage increase specified.) The most desirable relationship between these parameters is a sufficiently long scorch time to allow the compositions to be processed before start of cure, followed by a rapid cure. Provided the scorch time is adequate for handling, the smaller the t 90 to t s 2 ratio, the better the cure procedure. Since the compositions of the present invention mask the scorch effect of water, storage accompanied by the absorption of water does not affect the cure conditions. Thus, the cure/scorch time ratio of a composition of the present invention does not change significantly during storage, i.e., 1, 4, 7, days or more at ambient conditions of about 23° and 50° relative humidity. By "does not change significantly" it is meant that the t 90 /t s 2 ratio does not change after 1, 4 and 7 days by more than about 35%, preferably not more than about 20%, and most preferably by not more than about 5%. (In other words, the compositions of this invention are capable of being stored for these periods of time with no more than the percentage increase specified.) (While the tests presented herein are specific with respect to temperature and humidity, it should be understood that the vulcanizable compositions may be stored at temperatures and relative humidity normally encountered in commercial practice. Such relative humidities may typically range from about 20% to 100%.) One additional advantage of the instant invention with respect to compositions comprising chlorinated polyethylene polymer is that t 90 /t s 2 ratios below 4, preferably below 3, may be achieved. Table I gives the ingredients in phr of compositions A and B used in Examples 1 to 5, excluding crosslinking agents 2-mercapto-1,3,4-thiadiazole-5-thiobenzoate ("ECHO" A, made by Hercules Incorporated, Wilmington, DE), and GLY (Glycerin, U.S.P., J.T. Baker, Inc., Phillipsburg, NJ). Chlorinated polyethylene (CPE) polymer containing 36% chlorine was used (Tyrin CM 0136, Dow Chemical Co., Plaquemine, LA). Ingredient Composition A Composition B CPE 100 100 carbon black, N550 50 -- carbon black, N762 -- 50 Plasticizer A 35 -- Plasticizer B -- 30 Magnesium Oxide 5 10 Stabilizer 2 -- Amine Accelerator 1.15 1 In the tables of the examples, T min is the torque in lbf.in when the composition reaches its minimum torque as the viscosity of the composition in the ODR decreases on heating before significant crosslinking. T max is the torque when maximum cure is reached, as indicated by no further torque increase with further heating time. ΔT is the difference from minimum to maximum torque (100% cure); t 90 and t s 2 are defined above. Motor time is the time for the recorder pen of the data plotter to traverse the plotting span of the recorder paper, starting at the closing of the ODR cavity. The maximum cure rate represents the greatest increase in torque units per unit time during the cure cycle. It is the maximum slope of the cure curve during curing. EXAMPLE 1 This example demonstrates the effect of aging and moisture on the vulcanization of CPE formulated with "ECHO" A (Tables 2 and 3), and with "ECHO" A and GLY (Tables 4 and 5). The compositions used in the tests of Tables 2,3,4 and 5 contained 193.15 phr of composition A (Table I) formulated with 2 phr of "ECHO" A; 1.75 phr of GLY was also formulated into the compositions for the tests of Tables 4 and 5. The tests were made using (38 mm x 38 mm x 6 mm) (1 1/2" X 1 1/2" X 1/4") squares of pressed compositions aged in a desiccator at room temperature over anhydrous calcium sulfate (Tables 2 and 4 - Dry Aging) and over water (Tables 3 and 5 - Humid Aging). After aging, samples used in the tests of Tables 2 and 3 (no GLY) were vulcanized in a ODR at 177°C (350°F), 3° arc and 100 cpm; samples used in the tests of Tables 4 and 5 (with GLY) were vulcanized at 360°F, 3° arc and 100 cpm. DRY AGING (NO GLY) Test # 1 2 3 4 Days Aged 0 1 3 7 Weight Increase % -- 0 0 0 T min 10.0 9.9 10.2 10.8 T max 36.0 34.0 33.5 34.0 ΔT 26.0 24.1 23.3 23.2 t s 2 7.9 7.8 7.8 7.1 t 90 39.3 36.8 42.0 41.6 t 90 /t s 2 5.0 4.7 5.4 5.9 HUMID AGING (NO GLY) Test # 1 2 3 4 Days Aged 0 1 3 7 Weight Increase % -- 0.3 0.6 1.1 T min 10.0 10.5 11.9 15.1 T max 36.0 53.8 56.2 60.0 ΔT 26.0 43.3 46.3 44.9 t s 2 7.9 4.3 3.2 2.2 t 90 39.3 21.8 18.0 13.0 t 90 /t s 2 5.0 5.1 5.6 5.9 DRY AGING (WITH GLY) Test # 9 10 11 12 13 Days Aged 0 0.67 1 4 7 Weight Increase % -- 0 0 0 0 T min 7.8 8.0 8.0 8.2 8.3 T max 53.0 52.1 52.0 50.8 51.0 ΔT 45.2 44.1 44.0 42.6 42.7 t s 2 1.5 1.6 1.55 1.45 1.4 t 90 4.0 3.9 3.9 3.6 3.6 t 90 /t s 2 2.7 2.4 2.5 2.5 2.6 HUMID AGING (WITH GLY) Test # 14 15 16 17 18 Days Aged 0 0.67 1 4 7 Weight Increase % 0 0.25 0.33 0.88 1.54 T min 7.8 8.1 8.1 8.8 9.1 T max 53.0 52.0 52.0 52.2 50.3 ΔT 45.2 43.9 43.9 43.4 41.2 t s 2 1.5 1.55 1.45 1.3 1.25 t 90 4.0 3.8 3.6 3.6 4.3 t 90 /t s 2 2.7 2.5 2.5 2.8 3.4 As can be seen in Table 3, humid aging of conventional compositions has a very significant effect on curing parameters-note particularly how the ΔT increases and, t s 2 and t 90 times decrease with aging (Table 3). Dry aging (Table 2) has no apparent effect. Table 5 shows that the inclusion into Composition A (containing "ECHO" A) of GLY Substantially completely masks the effect of water on aging - note particularly how the ΔT, t s 2 and t 90 times are substantially unaffected by humid aging. Dry aging (Table 4) has no apparent effect. These data are plotted on the graphs of Figures 1 and 2. The data on the conventional compositions, Figure 1, show that the humid samples stored over water had undergone significant pre-vulcanization scorching during storage, as shown by the decreasing scorch times t s 2 and cure times t 90 as storage time increased. The dry samples showed no such scorch and cure time changes. This series of tests confirms that relative humidity during storage greatly affects the curing requirements of crosslinking halogen-containing polymer. In contrast, the data on the present invention compositions (Figure 2) shows that the relative humidity during storage has no noticeable effect on either scorch or cure time. The presence of the GLY along with "ECHO" in the present invention compositions completely masks the effect of water in the composition. For this reason, uniform vulcanizates are obtained batch to batch and after storing the same batch irrespective of water content of the material. In contrast, the conventional compositions of Figure 1 are greatly affected by storage at humid conditions; batches of the same ingredients stored the same time at the same temperature, but at different relative humidity will respond differently to a standard cure cycle and will give variable properties in the vulcanization. As can be seen in Table 5, the compositions of the present invention aged at room temperature and 100% relative humidity absorb significant amounts of water, approximately 0.25, 0.33, 0.88 and 1.54% weight increase of the composition respectively after storage for 0.67, 1, 4 and 7 days. At lower relative humidity the percent water absorption would be less. However, after storage at any relative humidity some water will be present in the compositions. The amount of absorbed water increases as the storage time increases. Thus, since some water is normally present in the air during storage, the stored compositions of the present invention will contain water from a trace to as much as 2% by weight or more (normally greater than about 0.05% by weight, more typically from about 0.05 to 2% by weight, and often about 0.2% to 2% by weight). The stored compositions will comprise vulcanizable halogen-containing polymer; 2-mercapto-1,3,4-thiadiazole-5-thiobenzoate; GLY and a small amount of water. Note that this small amount of water is sufficient to cause scorching in the conventional samples of Figure 1. EXAMPLE 2 - EFFECT OF WATER IN THE COMPOSITION The effect of adding water to the vulcanizable compositions is shown in Table 6. 193.15 parts of Composition A plus 2 phr of "ECHO" A were used in Test 19 and 20; Test 19 composition also contained 5 phr of GLY and no added water; Test 20 also contained 4.55 phr of GLY and 0.45 phr of added water. Test 19 and 20 were vulcanized using a ODR at 182°C (360°F), 3° arc, 100 cpm, and 12 minute motor time with the following results: ODR CURE DATA Test # 19 20 T min 4.9 6.1 T max 50.6 50.2 ΔT 45.7 44.1 t s 2 1.05 1.1 t 90 4.6 4.5 t 90 /t s 2 4.4 4.1 These tests show that the addition of small amounts of water to the compositions of the present invention has no significant effect on the curing times. Like the Table 5 results, these results are obtainable in batch to batch replications of these tests. EXAMPLE 3 This example illustrates in Tests 23-27 the preferred practice of the present invention. The compositions of Example 3 consist of 193.15 parts of composition A of Table I and contain 2 phr "ECHO" A; Tests 21 and 22 contain no GLY; Tests 23-27 contain 1.75 phr of GLY. Tests 23-27 demonstrate the excellent curability of the vulcanizable compositions of the present invention as compared to Tests 21 and 22, which do not contain GLY. Curing was carried out in these examples using an ODR at 182°C (360°F), 3° arc and 100 cpm. These tests were performed on unstored, freshly formulated compositions. The curing results are shown in Table 7. ODR CURE DATA Test # 21 22 23 24 25 26 27 T min 6.1 5.0 7.8 4.5 5.0 6.8 5.1 T max 39.2 41.1 53.0 46.2 49.3 50.8 48.9 ΔT 33.1 36.1 45.2 41.7 44.3 44.0 43.8 t s 2 2.5 2.7 1.5 1.65 1.8 1.67 1.9 t 90 29.0 25.0 4.0 4.6 4.8 4.4 5.0 t 90 /t s 2 11.6 9.3 2.7 2.8 2.7 2.6 2.6 In Tests 23-27 all of the scorch times of the present invention compositions were adequate and all of the t 90 /t s 2 ratios were less than the preferred maximum of 3. Of particular importance are the extremely rapid t 90 times for the compositions of the present invention containing both "ECHO" A and GLY. EXAMPLE 4 - PHYSICAL PROPERTIES The tests of this example show the physical properties of vulcanizates from unaged compositions of the present invention press cured five minutes at 182°C (360°F). All of the tests used 191 phr mixture B from Table 1 and contained 2 phr of "ECHO" A. Test 28 contained no glycerin; Test 29-32 contained 1.75 phr GLY. In Table 8, M100, M200 and M300 are the psi (1 psi is equivalent to 6.9 kPa) required to extend the vulcanized test samples 100, 200 and 300% respectively; TB is the tensile strength at break; EB is the % elongation at break, and Hardness is Shore A. PHYSICAL PROPERTIES Test # 28 29 30 31 32 M100 560 620 670 620 640 M200 1160 1270 1380 1280 1430 M300 1630 1750 1880 1820 2020 TB 2140 2150 2320 2350 2440 EB 450 400 420 430 400 Hardness 70 71 71 73 73 EXAMPLE 5 - EPICHLOROHYDRIN POLYMERS This Example shows the practice of the present invention with epichlorohydrin polymers. The polyepichlorohydrin polymer was Hydrin H from Zeon Chemicals USA, Inc., Louisville, KY. The epichlorohydrin-ethylene oxide copolymer was the 1:1 molar polymer available as Hydrin C from Zeon Chemicals USA, Inc. The compositions shown in Table 9 were vulcanized in an ODR at 171°C (340°F), 3° arc, 100 cpm. Table 9 also lists the ODR cure times. Tests 34 and 36, which contain 2.0 phr GLY, cured more rapidly (shorter t 90 ) and completely (higher ΔTorque) than the control compositions, Tests 33 and 35, which did not contain GLY. COMPOSITIONS (PARTS BY WEIGHT) Test 33 34 35 36 polyepichlorohydrin -- -- 100 100 epichlorohydrin-ethylene oxide copolymer 100 100 -- -- carbon black, N550 50 50 50 50 stearic acid 1 1 1 1 nickel dibutyldithiocarbonate 0.5 0.5 0.5 0.5 nickel dimethyldithiocarbonate 1.0 1.0 1.0 1.0 barium carbonate 5.0 5.0 -- -- magnesium oxide -- -- 5.0 5.0 "ECHO" A 2.8 2.8 2.8 2.8 GLY T min --11.6 2.0 9.6 --9.6 2.0 5.6 ODR CURE DATA T min 11.6 9.6 9.6 5.6 T max 121.6 136.0 114.2 120.4 ΔTorque 110.0 126.4 104.6 114.8 t s 2 2.4 1.3 6.3 2.5 T 90 42.8 18.4 88.5 30.3 EXAMPLE 6 - POLYACRYLATE RUBBER This example shows the practice of the present invention with polyacrylate rubber (a copolymer of ethyl acrylate and a chloroalkyl acrylate containing about 1-4% chlorine, available as Nipol AR 71 from Zeon Chemicals USA, Inc., Louisville, KY). The compositions of both tests contained 100 parts polyacrylate rubber; 50 parts carbon black, N330; 1.0 parts of stearic acid; 2.0 parts of diphenylamine/acetone reaction product; 10 parts of magnesium oxide; and 1.5 parts of "ECHO" A. Test 37 contained no GLY; Test 38 contained 2.0 parts of GLY. The compositions were vulcanized in an ODR at 182°C (360°F), 3° arc and 100 cpm with a motor run time of 30 minutes. Table 10 lists the ODR cure data. Test 38, which contained 2 phr GLY, cured more rapidly (shorter t 90 ) and completely (higher ΔTorque) than the control composition, Test 37, which did not contain GLY. ODR CURE DATA Test # 37 38 T min 12.0 13.5 T max 53 9 69.9 ΔTorque 41.9 56.4 t s 2 2.8 0.9 t 90 42.3 23.0 EXAMPLE 7 - CHLOROSULFONATED POLYETHYLENE This example shows the practice of the present invention with chlorosulfonated polyethylene. The chlorosulfonated polyethylene contained 35% chlorine and 1% sulfur (Hypalon 40, E.I. DuPont de Nemours and Co., Wilmington, DE). The compositions of both tests contained 100 parts chlorosulfonated polyethylene; 40 parts of carbon black, N774; 10 parts of aromatic oil; 1.0 parts of stearic acid; 5.0 parts of magnesium oxide; and 2.5 parts of "ECHO" A. Test 39 contained no GLY; Test 40 contained 2.0 parts of GLY. The compositions were vulcanized in an ODR at 171°C (340°F), 3° arc, 100 cpm. Table 11 lists the ODR cure data. Test 40, which contained 2.0 phr GLY, cured more rapidly (lower t 90 ) and completely (higher ΔTorque) than the control composition, Test 39, which did not contain GLY. ODR CURE DATA Test # 39 40 T max 11.2 10.0 T min 69 7 86.0 ΔTorque 58.5 76.0 t s 2 0.93 0.66 t 90 7.9 5.6 EXAMPLE 8 - POLYCHLOROPRENE RUBBER This example shows the practice of the present invention with polychloroprene rubber. The compositions of both tests contained 100 parts of polychloroprene rubber (Neoprene W, E. I. DuPont de Nemours and Co., Wilmington, DE); 50 parts of carbon black, N762; 10 parts of aromatic oil; 5 parts of barium carbonate; 0.5 parts of stearic acid; and 1.5 parts of "ECHO" A. Test 41 contained no GLY; Test 42 contained 2.0 parts GLY. The compositions were vulcanized in an ODR at 153°C (307°F), 3° arc and 100 cpm with a motor run time of 60 minutes. Table 12 lists the ODR cure data. Both products were acceptable vulcanizates. Test 42, which contained 2.0 phr GLY, had a desirable longer scorch time (t s 2) and about the same cure time (t 90 ) as the control composition (Test 41), which did not contain GLY. GLY appeared to plasticize the composition, based on the lower T min and T max of Test 42. ODR CURE DATA Test # 41 42 T min 13.0 10.0 T max 112.0 96.0 Δ Torque 99.0 86.0 t s 2 1. 2.5 t 90 35.3 33.8 EXAMPLE 9 - HALOBUTYL RUBBER This example shows the practice of the present invention with halobutyl rubber. The compositions of all of the tests contained 50 parts of carbon black, N330; 1.0 parts of stearic acid; 5.0 parts of stearic acid; 1.0 parts of N-phenyl-3,5-diethyl-2-propyl-1, 4-dihydropyridine; and 2.5 parts of "ECHO" A. Tests 43 and 44 contained 100 parts of bromobutyl rubber (containing 2.1% bromine, Bromobutyl 2030, Polysar Rubber Division, Miles, Inc., Sarnia, Ontario). Tests 45 and 46 contained 100 parts chlorobutyl rubber (containing 2 mol % unsaturation, Chlorobutyl 1066, Exxon Chemicals Americas, Linden, NJ). Tests 43 and 45 contained no GLY; Tests 44 and 46 contained 2.0 parts of GLY. The compositions were vulcanized in an ODR at 160°C (320°F), 3° arc and 100 cpm with a motor run time of 12 minutes. Table 13 lists the vulcanization times. All products were acceptable vulcanizates. ODR CURE DATA Test # 43 44 45 46 T min 15.9 17.0 14.3 14.5 T max 74.0 71.0 63.0 52.3 Torque 58.1 54.0 48.7 37.8 t s 2 1.0 0.9 2.3 2.0 t 90 22.2 33.2 43.0 44.2 EXAMPLE 10 - AGING AT 50% RELATIVE HUMIDITY AT 22°C (72°F), 12 MINUTE CURE CYCLE Compositions having the formulae shown in the following Table were prepared and compared. A masterbatch was prepared comprising all of the ingredients, except the crosslinking agent (1,3,4-thiadiozate-5-thiobenzoate) and GLY, and was mixed in a type B Banbury laboratory internal mixer. The crosslinking agent and, when used the GLY, were added on a laboratory differential speed two roll mill. The mixed rubber composition was cut into test pieces of approximately 32 mm x 32 mm x 6.4 mm (1 1/4 inches x 1 1/4 inches x 1/4 inch) suitable for cure evaluation in an Oscillating Disk Rheometer (ODR, Monsanto Model 100) and were tested using a standard 12 minute ODR run. Samples were tested the same day as prepared (0 days aging or unaged) or aged as specified in the tables and charts. Aging was at 50% relative humidity at 22°C (72°F). The times required for the unaged and 7 day aged sample to reach the same torque level on the cure curves was also recorded. The torque level was identified at the point where the cure rate of the unaged sample had dropped to 0.5. This data, presented in Table 15, as follows: The torque and time of the point on the cure curve of the unaged sample where the cure rate has decreased to half of its maximum value was identified. Then, on the cure curve obtained after 7 day aging, the point at which the torque is identical to the torque obtained at half the maximum cure rate of the unaged sample was identified. The time for the sample aged 7 days was divided by the time for the unaged sample to reach this torque level. The reduction in time is the percent reduction from the unaged time, for the 7 day sample to reach the torque when the cure rate of the unaged sample dropped to half the maximum cure rated, after the cure has passed through the maximum cure point. ACTIVATION OF CURE DATA RELATED TO INFLUENCE OF HUMID AGING ON CURE 47 Control 48 GLY Unaged R max ,(lb.in/min ) Nm/min (6.96) 0.8 (24.19) 2.8 R 0.5max , (lb.in/min ) Nm/min (3.48) 0.4 (12.1) 1.4 T 0.5max , (lb.in ) Nm (32.9) 3.8 (44.63) 5.1 t 0 , min 5.44 3.49 Aged t 7 /min 2.9 3.25 t 7 /t 0, % 53.4 93.2 Reduction in t 0-7 , % 46.6 6.8 Sample 47 did not reach full cure in 12 minutes. If a sample has not been completely cured, the Δ torque level (change in torque level) would be reported lower than actual, which would give lower t 90 and lower t 90 /t s 2. Therefore, data which depend upon full cure (Δ torque, t 90 , and t 90 /t s 2) were calculated using torque data at 12 min. cure in place of maximum torque. As a result, it is improper to compare those data from Samples 47 with the data of Sample 48 representing the invention. Because of the uncertainty of measuring t 90 for the control samples because they did not fully cure within the 12 minute test, the ODR cure plots and cure rate plots are better suited for evaluating the results of the experiment. The fact that only the GLY sample achieved full cure can be seen from Figures 3-4. The GLY sample achieved full cure as can be seen from the fact that torque became flat in the upper right corner. The control samples did not achieve full cure during the 12 minute test, as can be seen by the fact that the curves were still rising. Figures 3-4 show the ODR cure curves for unaged and aged samples of the control and invention. Figure 3 shows that the control samples experienced significant increases in scorch and cure rate after humid aging of 1, 3 and 7 days. Figure 4 shows that the GLY containing samples of the invention had much more consistent scorch times and cure rate upon humid aging than the control samples. Thus, the GLY samples of the invention would provide the most consistent scorch and cure rate properties and are best suited for commercial operations where inconsistent scorch and cure rate will lead to unsuitable products. Figures 5-6 support the above conclusions, the cure rate curve showing that the GLY sample is the only unaged sample to fully cure during the initial 12 minutes of the test and that the GLY has a higher maximum cure rate. From these Figures, we also see that the control samples show an increase in cure rate with exposure to moisture. Glycerin, on the other hand, shows a slight drop in cure rate. This is an indication that glycerin overrides the scorch effects of moisture on the cure. Figure 5 shows that with only crosslinker cure rate significantly increases and maximum cure time (the peak of the curve) decreases with humid aging. Most notable is the huge increase in the cure rate when the sample is aged. This shown by the peak of the curve. Figure 6 shows that GLY samples have a high cure rate. On humid aging the cure rate stays the same or slightly decreases with the invention whereas it increases with the control (Figure 5). Commercial operations can accommodate a slightly reduced cure rate more easily than they can handle a cure rate which increases over time. This is because the increased cure rate can not easily be accommodated. In contrast, the decreased cure rate can be handled by always using a slightly higher cure time than would be needed with the unaged composition. Thus using the invention the commercial practitioner is able to produce parts, with fewer or no parts needing to be discarded due to defects. Table 15 shows that based on the t 7 /t 0, % and reduction in t 0-7 , % cure time and cure rate were consistent with the GLY sample. That is, the torque value was much more consistent with the unaged and 7 day aged samples of the invention, than with the control sample. This data confirms that the invention masks the effects of humid aging on the compositions. EXAMPLE 11 - CURE OF CHLORINATED POLYETHYLENE AT 50% RELATIVE HUMIDITY USING 60 MINUTE ODR RUN These samples were tested using a 60 minute ODR run, since in other tests the control samples did not fully cure during the 12 minute ODR run normally used for this test. The procedures of Example 10 were repeated using a 60 minute ODR run. Using the 60 minute ODR test, it was possible to obtain data with the control samples that can be compared with the data from the invention samples. The above data shows that the invention provides very consistent scorch and cure rates upon humid aging, as compared to the control samples. Moreover, t 90 /t s 2 is relatively constant and is always less than 4. Thus, the data shows the significantly better results obtained with the claimed invention as compared to the control examples. ODR cure curves for unaged and aged samples of the control and invention, not presented herewith, show that the control samples did not fully cure during the first 12 minutes of the test verifying the data presented in Examples 10. The full 60 minute ODR plots shows that these samples did eventually cure. The ODR cure curves all confirm that the control samples experienced significant increases in scorch and cure rate after humid aging of 1, 3 and 7 days, whereas GLY containing samples of the invention had much more consistent scorch times and cure rate upon humid aging than the control samples. Similarly, cure rate curves (not presented herewith) showed that the GLY sample is the only unaged sample to fully cure during the initial 12 minutes of the test and that the GLY has a higher maximum cure rate than the control sample. From these plots, GLY samples show a slight drop in cure rate upon humid aging, whereas the cure rate increases upon humid aging with the control samples. This also confirms the data of example 10 and is an indication that glycerine overrides the scorch effects of moisture on the cure. Thus, for the reasons described in Example 10, using the invention the commercial practitioner is able to produce parts, with fewer or no parts needing to be discarded due to defects.

Claims: A process for reducing the effects of moisture during storage prior to vulcanization of a vulcanizable halogen-containing polymer composition containing water, comprising blending into said vulcanizable composition prior to storage, 0.1-20 parts by weight of a thioester derivative of 2,5-dimercapto-1,3,4-thiadiazole crosslinking agent and 0.1-20 parts by weight of glycerin, the amounts of the thioester derivative and glycerin being based upon 100 parts by weight of the halogen-containing polymer, the composition containing at least 0.05% by weight of water after storage at the start of vulcanization; whereby the scorch time t s 2 of the vulcanizable composition does not decrease by more than 30% after storage at ambient conditions of about 23°C and 50% relative humidity for 1 day as compared to the t s 2 of the unstored composition. A process according to Claim 1, wherein the composition contains 0.2-2% by weight of water at the start of vulcanization. A process according to Claim 1 or Claim 2, wherein the vulcanizable halogen-containing polymer is a homopolymer of epichlorohydrin; a copolymer of epichlorohydrin and ethylene oxide or propylene oxide; a terpolymer of epichlorohydrin, ethylene oxide or propylene oxide and an unsaturated alkylene oxide; polychloroprene; chlorosulfonated polyethylene; chlorinated high density polyethylene; a copolymer of alkyl acrylate and chloroalkyl acrylate; poly (vinyl fluoride); poly(vinyl chloride); poly(vinylidene chloride); chlorobutyl rubber; or bromobutyl rubber. A process according to Claim 3, wherein the vulcanizable halogen-containing polymer is a chlorinated polyethylene polymer. A process according to Claim 4, wherein the ratio t 90 /t s 2 for the composition is less than 4. A process according to Claim 5, wherein the ratio t 90 /t s 2 for the composition is less than 3. A process according to Claim 3, wherein the vulcanizable halogen-containing polymer is a polymer, copolymer or terpolymer of epichlorohydrin. A process according to Claim 3, wherein the vulcanizable halogen-containing polymer is a polyacrylate rubber. A process according to any preceding Claim, wherein said crosslinking agent is 2-mercapto-1,3,4-thiadiazole-5-thiobenzoate. A vulcanizable halogen-containing polymer composition comprising 0.1-20 parts by weight of a thioester derivative of 2,5-dimercapto-1,3,4-thiadiazole crosslinking agent, 0.1-20 parts by weight of glycerin, the amounts of the thioester derivative and glycerin being based upon 100 parts by weight of the halogen-containing polymer, and at least 0.05% by weight of water; whereby the scorch time t s 2 of the vulcanizable composition does not decrease by more than 30% after storage at ambient conditions of about 23°C and 50% relative humidity for 1 day as compared to the t s 2 of the unstored composition. A composition according to Claim 10, which comprises 0.2-2% of water. A composition according to Claim 10 or Claim 11, wherein the vulcanizable halogen-containing polymer is a homopolymer of epichlorohydrin; a copolymer of epichlorohydrin and ethylene oxide or propylene oxide; a terpolymer of epichlorohydrin, ethylene oxide or propylene oxide, and an unsaturated alkylene oxide; polychloroprene; chlorosulfonated polyethylene; chlorinated high density polyethylene; a copolymer of alkyl acrylate and chloroalkyl acrylate; poly(vinyl fluoride); poly(vinyl chloride); poly(vinylidene chloride) ; chlorobutyl rubber; or bromobutyl rubber. A composition according to Claim 12, wherein the vulcanizable halogen-containing polymer is a chlorinated polyethylene polymer. A composition according to Claim 13, whose ratio of t 90 /t s 2 is less than 4. A composition according to Claim 14, wherein the ratio of t 90 /t s 2 is less than 3. A composition according to Claim 12, wherein the vulcanizable halogen-containing polymer is a polymer, copolymer or terpolymer of epichlorohydrin. A composition according to Claim 12, wherein the vulcanizable halogen-containing polymer is a polyacrylate rubber. A composition in the form of a dry pourable powder cure premix composition for inclusion in a halogen-containing vulcanizable polymer composition, comprising a thioester derivative of 2,5-dimercapto-1,3,4-thiadiazole crosslinking agent, glycerin and a pourable siliceous finely divided filler. A composition according to any of Claims 10-18, wherein the crosslinking agent is 2-mercapto-1,3,4-thiadiazole-5-thiobenzoate. A process for reworking a vulcanizable halogen-containing polymer composition comprising sequentially blending before storage, into said vulcanizable composition, 0.1-20 parts by weight of a thioester derivative of 2,5-dimercapto-1,3,4-thiadiazole crosslinking agent and 0.1-20 parts by weight of glycerin, the amounts of the thioester derivative and glycerin being based upon 100 parts by weight of the halogen-containing polymer, storing the vulcanizable composition for one or more days after which it contains at least 0.05% by weight of water, testing a sample of the vulcanizable composition for the cure rate and/or scorch rate of the vulcanizable composition and the physical properties of the vulcanized halogen-containing polymer composition, and reformulating the vulcanizable composition by changing the relative amounts of the composition's ingredients or adding an ingredient. A process according to Claim 20, wherein the step of reformulating the vulcanizable composition comprises adjusting the concentration of the thioester derivative of 2,5-dimercapto-1,3,4-thiadiazole crosslinking agent and/or glycerin in the vulcanizable composition. A process according to Claim 20, wherein the vulcanizable composition comprises one or more additives selected from accelerators, acid acceptors, binders, stabilizers, fillers, extenders, pigments, plasticizers and softeners. A process according to Claim 22, wherein the step of reformulating the vulcanizable composition comprises adjusting the concentration of one or more of the additives in the vulcanizable composition.

Inventors: CLASS JAY BERNARD, CLASS, JAY BERNARD
Applicants: HERCULES INC, HERCULES INCORPORATED
Application year: 1994
Main classification: C08K5
IPC codes: C08L101, C08L27, C08K5, C08L71, C08F28, C08L23, C08K9